1. Field of the Invention
The present invention relates to zoom lens systems, imaging devices, and cameras. In particular, the present invention relates to: a zoom lens system in which even in a configuration that the overall length of lens system is short and the size is small, a wide view angle at a wide-angle limit and a high zooming ratio are obtained and still quick focusing is achieved and, in particular, high optical performance is obtained even in a close-object in-focus condition; an imaging device employing this zoom lens system; and a thin and compact camera employing this imaging device.
2. Description of the Background Art
In the conventional art, in cameras such as digital still cameras and digital video cameras employing an image sensor for photoelectric conversion (simply referred to as digital cameras, hereinafter), increasing demands are present for size reduction and performance improvement.
As zoom lens systems to be employed in digital cameras in which size reduction and performance improvement are achieved as described above, for example, various kinds of zoom lenses having at least a two-unit construction of negative and positive have been proposed in which a first lens unit having negative optical power and a second lens unit having positive optical power are arranged in order from the object side to the image side.
Japanese Laid-Open Patent Publication No. 2005-352428 discloses a zoom lens having a four-unit construction of negative, positive, negative, and positive and achieving magnification change by changing air spaces between individual lens units, wherein in zooming from a wide-angle limit to a telephoto limit, the interval between the first lens unit and the second lens unit is changed so that magnification change is achieved, and wherein the first lens unit is composed of three lenses, the second lens unit is composed of four lenses, the third lens unit is composed of three lenses, and the fourth lens unit is composed of one lens.
Japanese Laid-Open Patent Publication No. 2008-197176 discloses a zoom lens having a four-unit construction of negative, positive, negative, and positive and achieving magnification change by changing air spaces between individual lens units, wherein in zooming from a wide-angle limit to a telephoto limit, the interval between the first lens unit and the second lens unit is changed so that magnification change is achieved, and wherein the first lens unit is composed of three lenses, the second lens unit is composed of three lenses, the third lens unit is composed of three lenses, and the fourth lens unit is composed of one lens.
Japanese Laid-Open Patent Publication No. 2010-122625 discloses a zoom lens having a three-unit construction of negative, positive, and positive and achieving magnification change by changing air spaces between individual lens units, wherein in zooming from a wide-angle limit to a telephoto limit, the interval between the first lens unit and the second lens unit is changed so that magnification change is achieved, and wherein the first lens unit is composed of two lenses, the second lens unit is composed of three lenses, and the third lens unit is composed of one lens.
Nevertheless, each of the zoom lenses disclosed in Japanese Laid-Open Patent Publication Nos. 2005-352428 and 2008-197176 includes ten or more lenses. This causes a high lens cost and further an increased overall length of lens system. Thus, requirements for digital cameras in recent years are not satisfied.
The zoom lens disclosed in Japanese Laid-Open Patent Publication No. 2010-122625 has lenses in a number as small as six, but still has an increased overall length of lens system. Thus, requirements for digital cameras in recent years are similarly not satisfied.